1. Field of the Invention
The present invention relates to a motor control method and device thereof, and more particularly to control methods and devices for improving a motor control signal to increase the operating performance of a motor.
2. Description of the Related Art
Today, motor control methods are sophisticated and advanced technology of utilizing circuits to control motor rotation has been provided. Furthermore, circuits are used to change or limit motor rotational speed, along with other functionalities of motor control. A well-known motor control device is shown in FIG. 1. The hall sensor 12 of the motor control device 1 detects a phase signal generated during the operation of the motor, and the phase signal is equal to the phase switched by a coil set 20 of the motor. The motor driver 10 is electrically coupled to the Hall sensor 12, receives the phase signal from Hall sensor 12 to generate a motor control signal. FIG. 2 shows the waveform of motor control signal 21. Ordinate A designates the amplitude of waveform, which can be represented as a voltage, while abscissa t designates time. Meanwhile, the coil switching circuit 14 often consists of two MOS switches. When the motor control signal 21 between two adjacent phases of current generated by the motor driver 10 is input into the coil switching circuit 14, the coil switching circuit 14 will output the motor control signal 21 sequentially into the motor coil set 20 to switch the current flow of to sustain motor rotation. Moreover, the PWM generating circuit 16 can modulate the motor control signal 21 as uniform-distributed rectangular waves by way of the pulse width modulation (PWM). Referring to FIG. 3. After the motor control signal 21 is divided into several small rectangular waves, the motor control signal 21 is equalized to smaller amplitude according to the equivalent principle. Inputting the equivalent motor control signal 21 into the motor coil set 20 will slow the motor rotational speed. Conventional motor driving methods use fixed duty cycle to turn on or off the coil switching circuit 14 to control the motor rotational speed. The current signal 22 is shown in FIG. 4. Ordinate A designates the amplitude of waveform, which can be represented as a current, and abscissa t designates time. FIG. 4 shows that current peaks at P1 and P2 have very high current during polarity switching, and these two current peaks result from the fact that inducing element (motor coil set 20) stores or releases energy during electrical conduction. The efficiency and current status of the motor, however, are not optimal for conventional motor driving. For example, in FIG. 4 the operating efficiency of the motor in concave area P is worse than that in other areas. Accordingly, the operating efficiency could be optimal if the current is similar to direct current.